The Rex

I'm asking this question for a guy I work with. He has a 96 LT1. The problem he's having is the cooling fans won't come on unless he turns on the A/C or heater. He's done some diag and found the fans come on when he disconnects the fan switch. He also says he's getting no voltage to the switch. I know the info I have might be a little thin, but I talked to him yesterday. If you need more info I can get it. I'm asking becuse he's a lurker, but not a member. I'm trying to correct that. Thanks for the help ya'll. :cheers:

ShawnZR-1

That's a bit sketchy all right. There is no fan switch, there is an ECT at the water pump though. The ECM reads that for the water temp and (among other factors) decides when to turn the fans on.

One question I have is when does he expect the fans to come on? Remember, on the LT1, the primary doesn't come on until 218* (I think) and the second at 224*. In any case, it has to be really hot! I remember testing my fans getting quite worried as that needle approached the shaded zone, but sure enough, the primary fan kicked on and arrested the climb.

There are changes in the prom that can be made to turn the fans on earlier, contact Craig (Marcho Polo), he can whack a chip out in no time. :cheers:

[EDIT] By the way, the reason the fans kicked on when the sensor was disconnected is because the ECM detected a failure and went into limp mode. When it does that, the fans turn on and it comes out of closed loop so you can limp home. The fact that it did this tells me that particular sensor is probably good. [/EDIT]


[Modified by ShawnZR-1, 8:54 AM 3/6/2003]

94 Red Roadster

I agree with Shawn that there may not really be a problem. Just like to add that there are several aftermarket fan switches which turn the fans on at lower temperatures. You can check it out in Ecklers, midAmerica, etc.

96GS#007

Check the temps. The '96 fans are programmed to come on at 219*. Due to CRS, I can't remember if both fans or only the primary fan come on at that temp. It's in the Factory Service Manual. He has one of those right? :)

He should use the digital temp readout versus the analog. The digital temp gets its feed via the PCM. It uses the sensor that's installed in the waterpump. This is also the input the PCM uses to control the fans. The analog gauge uses a feed from the sensor screwed into the passenger side cylinder head (between the #6 & #8 plugs). Because of the different sensors and their locations, the readings can be and usually are different.

Regarding a fan switch. Most are for '95 and older. '96 has a slightly different set-up, so be careful to purchase the correct one.

The Rex

It was the sensor he disconnected(I appologize about the misprint. I was pretty hung over this morning :banghead: ) He says the fans don't come on at all. He replaced the relays & sensors with no effect. He has a periodic ck engine light that comes on for a bit & then goes away. He pulled faults & got a code 16(he thinks that's what it was). I appreciate the help. Let me know what other info might help with guestimates. I'm playing middle man here. Thanks ya'll.

96GS#007

To pull the codes out of a '96, he needs a scan tool or scan software on a laptop. ALL PCM codes will start with P####, with P being for PCM and # representing the DTC number. For example, P0300 is Random Misfire. It would appear that he pulled the CCM codes.

Before he throws too much money away, he ought to take it somewhere and really find out what the code is.

ShawnZR-1

Wait a sec, a little clarification:
Your first post said he can get the fans to come on with the A/C, but the last post says he can't get them to come on at all. Which one is more correct?

I'm asking because if it is the latter (they don't come on at all), then he needs to start checking wiring between the PCM and the fan control circuit. If he can get the fans on by using the A/C, but still not when the temp reaches 220*, then the problem lies back at the PCM (if the guages read correctly). How long has he owned the car? I still suspect that he isn't letting it get hot enough to allow them to come on automatically.

The Rex

I meant the fans don't come on at all unlees you turn on the a/c or heat, or disconnect the sensor. I appologize about the confusion, but I'm playing middle-man here. The guy bought it used. I'm just trying to help him out.

ShawnZR-1

Ok, enough, tell him to register here. It will cut down on the confusion. Have you actually seen what happens? Does he let the car get really damn hot before he says things aren't working? I think we've all done the same thing, thinking the fans can't be working when the needle is pointing at 220*, then WHEW, they turn on. :yesnod: Really, it is a new C4 owners ritual.

96GS#007

:lolg: :yesnod: :lolg:

The Rex

:iagree: I went through it too. I haven't checked the car myself. I'm just going by what he says. Your right, he needs to register. Thanks for the help anyway.